Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.60	13.515%	$7.492	$7.49	$7.50	$7.50
Purchase #2	$69.48	12.640%	$78.2623	$78.26	$78.25	$78.30
Purchase #3	$181.90	12.664%	$204.9358	$204.94	$204.95	$204.90
Purchase #4	$172.77	8.446%	$187.3622	$187.36	$187.35	$187.40
Purchase #5	$233.58	9.398%	$255.5318	$255.53	$255.55	$255.50
Purchase #6	$16.69	10.217%	$18.3952	$18.40	$18.40	$18.40
Purchase #7	$16.59	9.802%	$18.2162	$18.22	$18.20	$18.20
7 purchase totals =	$697.61		$770.1955	$770.20	$770.20	$770.20